ShowCalibrator is a software utility that easily creates line-up slides for multiple display configurations. It compensates for any off-set (overlap or separation) between displays or projectors and can as such be used for projectors, LCD-displays and LED-walls.
The program even calculates the physical screen size based on the canvas used and provides position data for displays in animation programs like Watchout.
Please check out the online tutorial that covers all features of ShowCalibrator
You can take a look at some test samples below. The green/red vertical lines are indicating positions of right and left edges of displays/projectors (green is right/starboard in marine terms etc.).